Production of aromatic compounds



United States Patent PRODUCTION OF AROMATIC' COMPOUNDS.

Edwin Marvin Smolin, Stamford, James Kenneth Dix'on, Riverside, andKenneth Worden Saunders, Darien, Conn., assignors to American CyanamidCompany, New York, N.Y., a corporation of Maine No Drawing. Filed June23,1954, SenNo. 438,876

10 Claims. cram-669 This invention relates to the production of arylcompounds having at least one aliphatic nuclear substituent whichcontains a carbon-to-carbon double bond and, more particularly, to theproduction of such aryl compounds as those which have a vinyl groupattached to an aryl nucleus.

Methods of producing styrenes and pounds made in accordance withthepIesent invention have been previously disclosed as, for example, inthe Sturrock and Lawe U.S. Patent No. 2,373,982, which issued April 17,1945. This patent deals with the use of silicious catalyst and, moreparticularly, hydrated aluminum silicate catalyst. Modifiedalumina-silica catalystshave also been disclosed as, for example, in theDixon US. Patent Nos. 2,422,163-5 wherein such modifiers as titania,zirconia and thoriahave been employed.

An object of the present invention is to provide improved catalystswhich are efiective for the conversion of diaryl substituted paraflin,having at least two carbon' atoms in the paralfin chain and having thearyl groups attached to the same carbon atom, into two aromaticcompounds including one which has an aliphatic nuclear substituentcontaining a carbon-to-carbon doublexbond. This and other objects of ourinvention are attained by employing a boria-alumina-silica catalyst.Thus, the present process contemplates contacting a vapor comprising acompound of the class consisting of parafiins having at least two carbonatoms and having'two aryl substituents attached to one of said carbonatoms and their nuclear substituted derivatives with aboria-aluminasilica catalyst at a temperature of at least 350 C. andpreferably at a temperature of 500-600" C. It is preferable that thecontact time of the vaporous paraiiin with the catalyst be less than 0.8second and, in order to avoid practical difficulties, it is generallydesirable to em-- ploy a contact time of 0.001 second or more. Still an2 v 1 15 parts per hour of 1,1-ditolylethane diluted witha IOO-molexcess of steam were passed over 345 parts of the catalyst. packed in atube. maintained at' a temperature of about 525 C.. The contact time ofthe reactants with the catalyst was 0.18 second. The conversion wasinitially 78% and, after 2 parts of 1,1-ditolylethane per part ofcatalyst had been fed, the conversion dropped" Methylstyrene. andtoluene obtained by the vention maybe'prepared synthetically bycoprecipitation ether aryl mof silica, boria and alumina to formahydrogel which is thereafter washed and" dried.- Still another method ofpreparation is to precipitate boria on a silica-alumina hydrogeL'or toprecipitate the alumina on a silica-boria hydrogel. Itis preferable thatthe gel be calcined-after drying, for example, at a temperature'of about1 50-650" C. or more. It isalso" possibl'e to precipitate boria'onnatural alumina-silicate such as kaolin. The proportions of boria to'silica alumina by weight may be varied.

widely but, in general, we prefer to use at least 1% by weight'otboriaand'the weight ratio of boriato-silic-a:

alumina'mayb e'varied.widely between about 1:99- and 99-: 1. For mostpurposes the proportion of silica-alumina is; in excess of theproportion of boria. Suitable boron compounds that'may easily beconverted to boric oxide solid ubstances which activate them and /or'which are I entirely inert. "Such substances may 'be used to extend,

the active surface of the boria-alumina-siiica catalysts;

or they may be used as supports for the catalysts. For example, thecatalysts employed in accordance with thisinvention may be'supportedupon finely-divided silicon carbide, non-porous aluminumioxide, highlyfired ceramic materials in the form of rings, saddles, grids and thelike. Binding agents such as sodium silicate may be advantageouslyemployed in some cases to improve the other feature of the presentprocess is the use of a:

diluent, preferably water vapor in relatively highpro portions, namely,from about 5 to about 150 or more mols of diluentper mol of thediarylsubstituted paratfin. Water vapor is one of the most desirablediluents since it pellets may be in any desiredshape such as cylinders,

may be easily condensed and thereby separated from the final product.

The following example in which the proportions are in parts by weight isgiven by way of illustration and not limitation. The diaryl substitutedpanafiin employed in the example is 1,1-ditolylethane.

Example A boria-alumina-silica catalystwas prepared as follows: asolution, of 21.2 parts of boric acid and 500; parts of water containing120 parts of suspended kaolin.

. tained at a temperature of about 120160 C. The catalyst coating was13.5% by weight of the'final catalystweight I r,

- in accordance with this invention. While longer contact v mechanicalstability of our catalysts.

Our catalysts are employed in a finely-divided condition fashionedinto'pellets which are preferably no larger than about 15 millimeters intheir greatest diameter. The,

spheres, rings. or of. an irregular granular shape. When large pelletsare employed, the vapor velocity varies widely between the center andoutside of the pellet and, therefore, the contact time at the center ofthe pellet is. longer than desirable. be as fine as possible in. orderto reduce the difference between the maximum and minimum vaporvelocities. which occur in the catalyst bed. Obviously, the particlesize. should not vbe so small that there is an excessive. pressure dropthrough the catalyst bed or so large, relative to thediameter of thecatalyst chamber, as to cause channeling through the bed.

The converter into which the catalyst is packed may be a tubeconstructed of steel, silica or any other suitable material and in largescale operations the converter may with the catalyst is desirable incarrying out the reactions;

It is preferable that the particles 7 i times may be use if desired, itis generally preferable that the contact time be less than 0.8 second.The contact times between about 0.1 and 0.05 are especially suitable.Generally, it is desirable to employ a contact time of l00l second orlonger inorder to avoid practical difficulties. The calculation of thecontact of the vapor with the catalyst is a complex matter and, in orderto simplify this calculation, we have used the term contact time hereinto mean those values which are computed on'the assumption that thecatalyst contains 50% voids and neglecting both the pressure dropthrough the catalyst and the increase in volume'which occurs during thereaction.

Inasmuch as the reaction is neither highly exothermic nor endothermic,it is not necessary to supply much more heat than that necessary tocompensate for conduction and radiation losses in order to maintain thereaction temperature of the vapors passing through the catalyst,providing the vapors which are fed to the catalyst are preheated toabout the desired reaction temperature and providing a high ratio ofdiluent to the diaryl parafii n is employed. We therefore prefer thatthe vapors fed to the catalyst be preheated to the reaction temperature.Any suitable method of heating the converter may be employed as, forexample, electrical resistance heaters.

The following are illustrative of the aliphatic compounds having twoaryl substituents attached to the same carbon atom thereof which may beconverted into the mononuclear aromatic compounds in accordance with thepresent invention: 1,1-diphenylethane; each of the 1-phenyl-l-tolylethanes; each of the 1,1-ditolylethanes; each of thel-phenyl-l-xylylethanes; each of the l-tolyl-lxylylethanes; each of the1,1-dixylylethanes; 1,l-diphenyl-. propane; each of thel-phenyl-l-tolylpropanes; each of the 1,1-ditolylpropanes; each of thel-tolyl-l-xylylpropanm; each of the 2,2-ditolylpropanes; each of the1,1- di(monochlorophenyl)-ethanes; each of the1,1-di(dichlorophenyD-e'thanes; each of the1,1-di(monohydroxyphenyl)-ethanes; each of l,1dicresylethanes; each ofthe 2,2-dicresylpropanes; each of the 1,1-dinaphthylethanes; each of the2,2-dinaphthylpropanes; each of the 1,1- dixenylethanes; each of the1-tolyl-l-naphthylethanes; and the like and their nuclear substitutedhalogen, hydroxyl and other derivatives all of which are volatile atthe-temperature and pressure used in the process. These substancescontaining tolyl, xylyl, cresyl, xenyl, monochlorophenyl anddichlorophenyl groups may be attached to the carbon atom of the paraflinchain at the ortho, meta or para positions and when two of these groupsare present they may be attached in the same or different positions.

The reaction temperature may be varied from about 350 C. up to about 600C., or even higher in some cases. Temperatures above 600 C. cause somepyrolysis loss but on the other hand some of the diaryl paraffins arenot easily decomposed at lower temperatures. It is particularlyimportant to employ a short time of contact when temperatures in theneighborhood of 600 C. are used in order to avoid an undesired amount ofpyrolysis loss due to side-reactions. Among such sidereactions are thosewhich lead to the formation of polynuclear compounds includinganthracene derivatives.

One of the advantages of employing a short contact time with catalystsis that the life thereof is prolonged. With contact times of the orderof one second or more the catalysts may become fouled in a relativelyshort period of time due to the deposition of carbonaceous materials onthe surface of the catalyst. When it is necessary or desirable toreactivate the catalyst, this may be done by passing heated air,preferably mixed with steam or carbon dioxide, through the catalyst. Thetemperature of the air and steam mixture should be raised to about500-650 C. The air enables the carbon to burn whereas the steam orcarbon dioxide which is temperature to the reaction temperature greatlysimplifies the change from normal operation to reactivation and back tonormal operation. Since the normal highly active life of the catalystgreatly exceeds the time required for its reactivation, the operation oftwo or more converters in parallel in readily accomplished. The shorttime of reactivation enables one to keep one or more converters innormal operation while one or more other converters are beingreactivated.

I Any material which is volatile and which does not react with thediaryl substituted paraffin which is to be used in accordance with ourprocess and which does not react with the products formed by thedecomposition of the diaryl substituted parafiin may be used as adiluent. Among these, some examples are: water, the hydrocarbons (suchas benzene and toluene), the fixed gases (such as nitrogen and carbondioxide), etc. Water vapor is the preferred diluent inasmuch as it maybe readily condensed and therefore separated from the products of thereaction, whereas the fixed gases or the hydrocarbons are somewhat morediflicult to separate from the product and such separation requireshigher expenditures than are required for the separation of water fromthe product. Water vapor also has an additional advantage in that it maymaintain the catalyst in highly active form.

One of the most important reasons for the use of a diluent is that thetime of contact of the diaryl substituted parafiin with the catalyst canbe reduced to the desired point easily. It has been found that in orderto obtain the short contact times which are desirable in accordance withthe present invention the molal ratio of diluent to the diarylsubstituted aliphatic compound in the feed to the catalyst is preferablybetween about 5:1 and 150:1, or more. If the feed can be suppliedrapidly enough to provide a low contact time without the use of thelarge proportion of diluent, the ratio of diluent to the diarylsubstituted paratfin may be as low as 1:2.

It has been found that it is fiequently desirable to convert only a fewpercent of the diaryl substituted parafiin fed to the catalyst in onepass but, by recovering the unconverted diaryl substituted paraffin andrecirculating it from one to five times or more, a high yield isobtained very economically.

Our process may be operated at elevated or reduced pressure and undersome conditions it may be particularly advantageous to operate underreduced pressure. If the diaryl substituted paraffin which is to be usedin accordance with present processes is not readily volatile at ordinarypressure, reduced pressures may be used to facilitate the operation ofour process.

The present process is a convenient and economical method of convertingthe diaryl substituted parafiins, having at least two carbon atoms inthe paraffin chain and having the two aryl groups attached to the samecarbon atom, into two aromatic compounds, one of which contains a sidechain having an ethylenic group. The vinyl substituted aryl compoundsprepared in accordance with the present invention have wide utility inthe production of polymers which in turn are useful for molding,casting, laminating and for many other purposes. Furthermore, pure arylcompounds such as xylene isomers in extremely high purity may beproduced simultaneously with the production of the aromatic compoundcontaining an ethylenic side chain. Thus, when a diaryl substitutedparaflin is cracked in accordance with this invention, one molecule ofan aryl compound having an ethylenic side chain is obtained togetherwith one molecule of an aryl compound which does not have an ethylenicside'chain. Such aryl compounds as, for example, m-xylene or p-xylene,find utility in the synthesis of organic compounds where the presence ofone or more of the possible isomers is undesired. This may be shown inthe production of a diaryl substituted parafiin by the reaction of amixture o-, mand p-xylenes and ethyl benzene with paraldehyde,acetaldehyde or acetylene. Here the meta isomer reacts preferentially,thus enriching the um'eacted mixture in the ortho and para isomers ofxylenes and also in ethyl benzene. p-Xylene may be recovered from thismixture by fractional crystallization methods apparent to those skilledin the art. Upon decomposition of the diaryl substituted paraffin ofthis synthesis, the aryl compound obtained which does not have anethylenic side chain will contain a predominant amount of m-xylene.

We claim:

1. A process of producing a plurality of aromatic compounds whichcomprises mixing an asymmetric diarylethane with a diluent, contactingthe resulting mixture thereof with a boron oxide alumina-silica catalystand maintaining the temperature of said mixture at a temperature whichwill cause said asymmetric diarylethane to decompose into a plurality ofaromatic compounds in the presence of a catalyst and which is at least350 C. during the contact time with said catalyst of between about 0.001second and about 0.8 second.

2. A process of producing a plurality of aromatic compounds whichcomprises mixing an asymmetric diarylethane with water vapor diluent,contacting the resulting mixture thereof with a boron oxidealumina-silica catalyst and maintaining the temperature of said mixtureat a temperature which will cause said asymmetric diarylethane todecompose into a plurality of aromatic compounds in the presence of acatalyst and which is at least 350 C. during the time it is in contactwith said catalyst.

3. In a method of producing a plurality of aromatic compounds, the stepwhich comprises contacting an asymmetric ditolylethane with a boronoxide-aluminasilica catalyst at a temperature which will cause saidditolylethane to decompose into a plurality of aromatic compounds in thepresence of a catalyst and which is at least 350 C. and for a contacttime of less than 0.8 second.

4. In a method of producing a plurality of aromatic compounds, the stepwhich comprises contacting 1,1- dixylylethane with a boronoxide-alumina-silica catalyst at a temperature which will cause saiddixylylethane to decompose into a plurality of aromatic compounds in thepresence of a catalyst and which is at least 350 C. and for a contacttime of less than 0.8 second.

least 350 C. and for a contact time of less than 0.8'

second, said diarylethane having at least one aryl group substitutedwith an alkyl group.

6. In a process for producing a plurality of aromatic compounds, thestep which comprises contacting an asymmetric diarylethane with a boronoxide-alumina-silica catalyst at a temperature which will cause saiddiarylethane to decompose into a plurality of aromatic compounds in thepresence of a catalyst and which is at least 350 C. and for a contacttime of less than 0.8 second, said diarylethane having at least one arylgroup substituted with a hydroxyl group.

7. In a process for producing a plurality of aromatic compounds, thestep which comprises contacting an asymmetric diarylethane with a boronoxide-alumina-silica catalyst at a temperature which will cause saiddiarylethane to decompose into a plurality of aromatic compounds in thepresence of -a catalyst and which is at least 350 C. and for a contacttime of less than 0.8 second, said diarylethane having at least one arylgroup substituted with an alkyl group and a hydroxyl group.

8. A process for producing vinyl substituted aryl compounds whichcomprises heating an asymmetric diarylethane at a temperature which isat least 350 C. and which will cause said diarylethane to decompose inthe presence of a boron oxide-alumina-silica catalyst.

9. A process for producing dimethylstyrene which comprises heating1,1-dixylylethane at a temperature which is at least 350 C. and whichwill cause said dixylylethane to decompose in the presence of a boronoxide-aluminasilica catalyst.

10. A process for producing methylstyrene which comprises heating1,1-ditolylethane at a temperature which is at least 350 C. and whichwill cause said ditolylethane to decompose in the presence of a boronoxide-aluminasilica catalyst.

References Cited in the file of this patent UNITED STATES PATENTS KropaSept. 29, 1953

1. A PROCESS OF PRODUCING A PLURALITY OF AROMATIC COMPOUNDS WHICHCOMPRISES MIXING AN ASYMMETRIC DIARYLETHANE WITH A DILUENT, CONTACTINGTHE RESULTING MIXTURE THEREOF WITH A BORON OXIDE ALUMINA-SILICA CATALYSTAND MAINTAINING THE TEMPERATURE OF SAID MIXTURE AT A TEMPERATURE WHICHWILL CAUSE SAID ASYMMETRIC DIARYLETHANE TO DECOMPOSE INTO A PLURALITY OFAROMATIC COMPOUNDS IN THE PRESENCE OF A CATALYST AND WHICH IS AT LEAST350*C. DURING THE CONTACT TIME WITH SAID CATALYST OF BETWEEN ABOUT 0.001SECOND AND ABOUT 0.8 SECOND.
 8. A PROCESS FOR PRODUCING VINYLSUBSTITUTED ARYL COMPOUNDS WHICH COMPRISES HEATING AN ASYMMETRICDIARYLETHANE AT A TEMPERATURE WHICH IS AT LEAST 350*C. AND WHICH WILLCAUSE SAID DIARYLETHANE TO DECOMPOSE IN THE PRESENCE OF A BORONOXIDE-ALUMINA-SILICA CATALYST.